Conventionally there are apparatuses for recognizing a character string printed on a surface of a medium such as a check. For example, in quite a few apparatuses for character string recognition commonly known; a character part is segmented along a circumscribing rectangular frame after detecting the character part from binarized image data, characteristic vectors are extracted from an obtained character pattern, similarity is calculated between the characteristic vectors of the entered character pattern and standard vectors of each character out of a characteristic dictionary, and then a candidate character(s) is selected according to a level of the similarity.
Some of those apparatuses for character string recognition include various means such as re-binarizing operation according to recognition results in order to improve recognition accuracy, and reading the medium again in case of failed reading operation (For example, refer to Patent Documents 1 through 3).
To describe more concretely; in a technology disclosed by Patent Document 1, character recognition is carried out again with image data binarized by using a different threshold value when normal character recognition results have not been obtained. In a technology disclosed by Patent Document 2, it is judged whether binary conversion of multilevel image is needed again or not, according to character recognition results and a result on the count number of black dots; and if needed, another threshold value being different from the initial one is set and the multilevel image is binarized again by using the threshold value newly set. In a technology disclosed by Patent Document 3, if recognition accuracy is lower than a prescribed requirement value, the character image is read again and then binary conversion is carried out by using a changed threshold value for binary conversion.
[Patent Document 1]
Japanese Unexamined Patent Publication (Kokai) No. JP2001-022884
[Patent Document 2]
Japanese Unexamined Patent Publication (Kokai) No. JP09-016715
[Patent Document 3]
Japanese Unexamined Patent Publication (Kokai) No. JP07-129713